//
//  PageViewController.swift
//  Landmarks
//
//  Created by yafei li on 2024/6/18.
//

import SwiftUI
import UIKit


struct PageViewController<Page: View>: UIViewControllerRepresentable {
    var pages: [Page]
    @Binding var currentPage: Int
    
    func makeCoordinator() -> Coordinator {
        Coordinator(self)
    }
    
    func makeUIViewController(context: Context) -> UIPageViewController {
        let pageViewController = UIPageViewController(
                    transitionStyle: .scroll,
                    navigationOrientation: .horizontal)
        pageViewController.dataSource = context.coordinator
        pageViewController.delegate = context.coordinator

        return pageViewController
    }
    
    func updateUIViewController(_ pageViewController: UIPageViewController, context: Context) {
        pageViewController.setViewControllers(
            [context.coordinator.controllers[currentPage]], direction: .forward, animated: true)
    }
    
    
    class Coordinator: NSObject,UIPageViewControllerDataSource,UIPageViewControllerDelegate {
       var parent: PageViewController
       var controllers = [UIViewController]()

       init(_ pageViewController: PageViewController) {
           parent = pageViewController
           controllers = parent.pages.map { UIHostingController(rootView: $0) }
       }
        
        func pageViewController(
            _ pageViewController: UIPageViewController,
            viewControllerBefore viewController: UIViewController) -> UIViewController?
        {
            guard let index = controllers.firstIndex(of: viewController) else {
                return nil
            }
            if index == 0 {
                return controllers.last
            }
            return controllers[index - 1]
        }


        func pageViewController(
            _ pageViewController: UIPageViewController,
            viewControllerAfter viewController: UIViewController) -> UIViewController?
        {
            guard let index = controllers.firstIndex(of: viewController) else {
                return nil
            }
            if index + 1 == controllers.count {
                return controllers.first
            }
            return controllers[index + 1]
        }
        
        func pageViewController(
                    _ pageViewController: UIPageViewController,
                    didFinishAnimating finished: Bool,
                    previousViewControllers: [UIViewController],
                    transitionCompleted completed: Bool) {
        if completed,
           let visibleViewController = pageViewController.viewControllers?.first,
           let index = controllers.firstIndex(of: visibleViewController) {
            parent.currentPage = index
        }
       }
    }
    
}

 
